In applications such as semiconductor processing, pressure control systems may be used to control pressure in a chamber. Pressure control valves are typically used, including but not limited to pendulum valves, butterfly valves, and throttle valves.
These valves may be controlled by a controller that uses different control algorithms. In particular, model-based control algorithms may be used that control the valves based on a pressure setpoint trajectory, and make compensations to the valve position to ensure that the actual pressure follows the pressure setpoint trajectory. When model-based control algorithms are used by the valve controller, various system parameters may have to be known, in order to optimize pressure control performance. These system parameters may include, but are not limited to, the volume of the chamber that encloses the fluid whose pressure is being controlled, and the pump speed curve of the valve that charts the pump speed (as controlled by the valve) of the system as a function of valve position.
Pressure control systems may typically require the end user to enter the chamber volume by hand. The user may not know, however, the accurate value of the chamber volume. If an incorrect chamber volume is input by the user, the pressure control performance may be compromised. Sub-optimal pressure control performance may result, including longer settling time, and larger overshoot or undershoot.
The valve controller may gather the actual pump speed curve using the existing algorithm without modification, which may result in the pump speed curve having slopes near zero. The near zero slope may require a high bandwidth of the valve motion controller. The actual bandwidth of the valve motion controller may be limited, however, resulting in an inadequate and oscillatory response.
A system and method are therefore needed for estimating proper chamber volume, and for optimizing the pump speed curve to improve pressure control performance.